U.S. patent number 9,417,018 [Application Number 14/385,394] was granted by the patent office on 2016-08-16 for multi-layer protective coating for an aluminum heat exchanger.
This patent grant is currently assigned to CARRIER CORPORATION. The grantee listed for this patent is Carrier Corporation. Invention is credited to Stephanie Bealing, Mark R. Jaworowski, Mary Teresa Lombardo, Matthew Patterson.
United States Patent |
9,417,018 |
Patterson , et al. |
August 16, 2016 |
Multi-layer protective coating for an aluminum heat exchanger
Abstract
A method for coating an aluminum alloy heat exchanger includes
subjecting at least one surface of the heat exchanger to a
pre-treatment process including cleaning; conversion coating the at
least one surface of the heat exchanger with a trivalent chromium
compound; and subjecting the at least one conversion coated surface
to an electro-coating in an aqueous solution containing an organic
corrosion inhibitor.
Inventors: |
Patterson; Matthew (Syracuse,
NY), Jaworowski; Mark R. (Glastonbury, CT), Lombardo;
Mary Teresa (Windsor, CT), Bealing; Stephanie (West
Hartford, CT) |
Applicant: |
Name |
City |
State |
Country |
Type |
Carrier Corporation |
Farmington |
CT |
US |
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Assignee: |
CARRIER CORPORATION
(Farmington, CT)
|
Family
ID: |
48048182 |
Appl.
No.: |
14/385,394 |
Filed: |
March 11, 2013 |
PCT
Filed: |
March 11, 2013 |
PCT No.: |
PCT/US2013/030132 |
371(c)(1),(2),(4) Date: |
September 15, 2014 |
PCT
Pub. No.: |
WO2013/138218 |
PCT
Pub. Date: |
September 19, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150034490 A1 |
Feb 5, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61611214 |
Mar 15, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C
22/83 (20130101); C23C 10/02 (20130101); C23C
22/34 (20130101); C09D 5/4488 (20130101); C23C
28/00 (20130101); C25D 13/20 (20130101); C25D
13/22 (20130101); F28F 19/06 (20130101); C09D
175/04 (20130101); C09D 7/61 (20180101); C09D
7/48 (20180101); C23C 10/24 (20130101); F28F
21/084 (20130101); C23C 2222/10 (20130101); C08K
2003/3045 (20130101); C08K 3/24 (20130101); C08G
2150/90 (20130101) |
Current International
Class: |
C23C
10/02 (20060101); F28F 19/06 (20060101); C09D
175/04 (20060101); C25D 13/22 (20060101); C09D
5/44 (20060101); C09D 7/12 (20060101); C23C
22/83 (20060101); C23C 22/34 (20060101); C25D
13/20 (20060101); F28F 21/08 (20060101); C23C
28/00 (20060101); C23C 10/24 (20060101); C08K
3/24 (20060101); C08K 3/30 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1739866 |
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Mar 2006 |
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CN |
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101321895 |
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Dec 2008 |
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CN |
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1992718 |
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Nov 2008 |
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EP |
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2009137358 |
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Nov 2009 |
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WO |
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2010045657 |
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Apr 2010 |
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WO |
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2011012443 |
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Feb 2011 |
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WO |
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2011037807 |
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Mar 2011 |
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WO |
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Primary Examiner: Mayekar; Kishor
Attorney, Agent or Firm: Cantor Colburn LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This patent application is a national stage of PCT Application
Serial No. PCT/US13/30132, filed Mar. 11, 2013, which claims
priority to U.S. Provisional Patent Application Ser. No.
61/611,214, filed Mar. 15, 2012, which is incorporated herein by
reference in their entirety
Claims
The invention claimed is:
1. A method for coating an aluminum alloy heat exchanger,
comprising: subjecting at least one surface of the heat exchanger
to a pre-treatment process including cleaning; conversion coating
the at least one surface of the heat exchanger with a trivalent
chromium compound; subjecting the at least one conversion coated
surface to an electro-coating in an aqueous solution containing an
organic corrosion inhibitor; and subjecting the at least one
electro-coated surface to a surface coating including application
of a top coat of a solvent borne coating composition comprising a
corrosion inhibiting pigment.
2. The method of claim 1, wherein the solvent borne coating
composition comprise as polyurethane.
3. The method of claim 1, wherein the conversion coating further
comprises immersing the heat exchanger in a conversion treatment
bath having dissolved species of a water soluble trivalent chromium
compound and a salt of hexafluorozirconic acid.
4. The method of claim 3, wherein the trivalent chromium compound
is trivalent chromium sulfate.
5. The method of claim 1, wherein the conversion coating further
comprises immersing the heat exchanger in a conversion treatment
bath for a predetermined contact time in an ambient temperature
environment.
6. The method of claim 1, wherein the conversion coating further
comprises spraying a solution containing the trivalent chromium
compound onto the at least one surface.
7. The method of claim 1, wherein the pre-treatment process further
comprises at least one of vapor degreasing using trichloroethylene
and solvent emulsion cleaning.
8. The method of claim 1, wherein the heat exchanger comprises
fins, tubes, or plates.
9. The method of claim 1, wherein the electro-coating further
comprises subjecting the heat exchanger to a cathodic
electro-coating with the heat exchanger being the cathode.
10. The method of claim 1, wherein the electro-coating further
comprises subjecting the heat exchanger to an anodic
electro-coating with the heat exchanger being the anode.
Description
FIELD OF INVENTION
The subject matter disclosed herein relates generally to the field
of deposition of coatings on an aluminum alloy heat exchanger and,
more particularly, to applying a multi-layer deposition of coatings
and corrosion inhibitors on an aluminum alloy heat exchanger that
provides an adherent multi-layered coating with substantial
corrosion resistance.
DESCRIPTION OF RELATED ART
Aluminum alloys are mixtures of aluminum with other metals (called
an alloy), often, zinc, manganese, silicon, copper, rare earths and
zirconium. Aluminum alloys are lightweight, have a high-specific
strength and a high-heat conductivity. Due to these excellent
mechanical properties, aluminum alloys are used as heat exchangers
for heating or cooling systems in commercial, industrial and marine
applications. Typical heat exchangers that use an aluminum alloy
material are fin, tube and plate heat exchangers.
However, aluminum alloy heat exchangers have a relatively high
susceptibility to corrosion. In severe marine applications,
particularly, sea water creates an aggressive chloride environment
in these heat exchangers. This chloride environment rapidly causes
pitting and corrosion of braze joints and fins as well as rupturing
refrigerant tubes. The corrosion eventually leads to a loss of
refrigerant and failure of the heating or system. To address the
issue, multi-layer coatings are applied to the aluminum alloy
through conventional methods like spraying or dipping in an attempt
to seal the surface from the corrosive environment. However, these
multi-layer coatings do not provide satisfactory adhesion
durability over the long-term. Additionally, these aluminum coating
methods have non-line-of-sight limitations. An improvement in
providing a multi-layer protection of an aluminum alloy heat
exchanger through coatings and inhibitors would be well received in
the art.
BRIEF SUMMARY
According to one aspect of the invention, a method for coating an
aluminum alloy heat exchanger includes subjecting at least one
surface of the heat exchanger to a pre-treatment process including
cleaning; conversion coating the at least one surface of the heat
exchanger with a trivalent chromium compound; and subjecting the at
least one conversion coated surface to an electro-coating in an
aqueous solution containing an organic corrosion inhibitor.
According to another aspect of the invention, a method for coating
an aluminum alloy heat exchanger includes subjecting at least one
surface of the heat exchanger to a pre-treatment process including
cleaning; conversion coating the at least one surface of the heat
exchanger with a trivalent chromium compound; subjecting the at
least one surface to an electro-coating in an aqueous solution
containing an organic corrosion inhibitor; and subjecting the
electro-coated heat exchanger to a surface coating including
application of a solvent borne solution containing a corrosion
inhibitive top coat.
Other aspects, features, and techniques of the invention will
become more apparent from the following description taken in
conjunction with the drawing.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawing in which:
FIG. 1 depicts a flow chart for an exemplary process of applying a
multi-layer coating on an aluminum alloy heat exchanger according
to an embodiment of the invention.
DETAILED DESCRIPTION
The present invention is more particularly described in the
following description and examples are intended to be illustrative
only since numerous modification and variations therein will be
apparent to those skilled in the art. As used in the specification
and in the claims, the singular form "a", "an" and "the" may
include plural referents unless the context clearly dictates
otherwise. Also, all ranges disclosed herein are inclusive of the
endpoints and are independently combinable.
Embodiments of a method for coating an aluminum heat exchanger
includes applying a combination of conversion coatings and
corrosion inhibitors through surface treatments and electrophoretic
deposition to provide an adherent multi-layered coating with
substantial corrosion resistance to the substrate of the heat
exchanger. In embodiments, the method provides applying a
multi-layer coating of a corrosion inhibitor on an aluminum alloy
heat exchanger including a surface pre-treatment of the heat
exchanger, a conversion coating, an electro-coating process and an
optional surface coating of the heat exchanger. The surface
pre-treatment includes at least one step to ensure that the surface
of the heat exchanger is clean and free of residues and foreign
materials. A coating process enables a film containing a trivalent
chromium compound to be uniformly coated on the aluminum alloy heat
exchanger substrate using an autocatalytic conversion coating
process. Further, the heat exchanger is electro-coated ("e-coated")
by applying a film containing corrosion inhibitors on the substrate
surface. Also, an optional topcoat application is applied to
supplement the corrosion protection on the surface in a solution
containing a corrosion inhibitor and polyurethane.
Referring now to the drawings, FIG. 1 illustrates an exemplary
process 10 of depositing multi-layer corrosion inhibitors on the
surface of a heat exchanger having an aluminum alloy substrate (or
substrate). Examples of such alloys include 1000, 3000, 5000, 6000
and 7000 series aluminum alloys. As used in the following
description, the surface of the heat exchanger may include, in some
non-limiting examples, fins, tubes and/or plates. As shown, the
exemplary process is initiated by surface pre-treatment 12 of the
substrate during which the substrate undergoes various treatments
to yield a surface character suitable for a subsequent conversion
coating process. The surface pre-treatment is not only used to
remove dirt and organic contaminants from the surface of the
aluminum alloy substrate, but also to remove an oxide or a
hydroxide formed on the aluminum alloy substrate thereby permitting
the surface of the substrate to be exposed for the conversion
coating process. According to one exemplary process, the substrate
preparation includes removing surface contaminants using a suitable
technique such as, in some non-limiting examples, solvent rinsing,
vapor degreasing using trichloroethylene or other suitable
solvents, solvent emulsion cleaning or the like in order to remove
any grease or organic compounds. In an exemplary embodiment, a
degreasing bath having an aqueous, non-silicate alkaline solution
containing a surfactant may be utilized to clean the substrate. In
an exemplary embodiment, the composition of the degreasing bath
includes non-silicate chemistry for removing any organic
contaminants from the surface of the substrate. In another
non-limiting embodiment, the surface pre-treatment may include an
elevated temperature soak in substantially pure water. As will be
appreciated by those of skill in the art, these surface
pre-treatment procedures are susceptible to a wide array of
alternatives. Thus, it is contemplated that any number of other
procedures and practices may likewise be utilized such as, for
example, by mechanical methods or by immersion or spray cleaner
systems in order to perform the pre-treatment process of the
substrate.
Following surface pre-treatment 12, the pre-treated substrate is
subjected to a corrosion inhibitive conversion coating 14 with a
trivalent chromium-containing layer in order to protect the surface
of the pre-treated heat exchanger from corrosion and enhance
adhesion of a corrosion inhibitive compound in a subsequent
electro-coating. The conversion treatment process is an
autocatalytic conversion coating process which is carried out by
immersing the pre-treated heat exchanger into the conversion
treatment bath for a predetermined contact time and temperature.
The treatment bath includes an aqueous solution having a salt of
hexafluorozirconic acid and a water soluble trivalent chromate
compound, which is free of hexavalent chromium. In one exemplary
embodiment, the trivalent chromate compound is trivalent chromium
sulfate. The water soluble trivalent chromate compound is present
in the aqueous solution in sufficient concentrations to coat the
surfaces of the pre-treated heat exchanger with a uniform layer of
trivalent chromium having an average thickness of 100 nm. In one
exemplary embodiment, the aqueous solution can include Surtec 650,
which is a commercially available liquid trivalent chromium based
chemical available from CST-SurTec, Inc. In a non-limiting
embodiment, the pre-treated heat exchanger is immersed for about 10
minutes at ambient temperature of about 30 degree Celsius (about
303 Kelvin) to about 40 degree Celsius (about 313 Kelvin) in order
to induce the conversion coating on the surface. In other
non-limiting embodiments, the aqueous solution may contain fluoride
and fluoborate. It is to be appreciated that the acidic fluoride
character of the conversion coating solution removes the native
oxide films and replaces it with hydrated Al--Zr--O--F layer, which
increases the hydrophilicity of the surface of the substrate and
activates the surface for organic coating. In an embodiment, the
conversion coated heat exchanger substrate is evaluated by visual
inspection. Thereafter, in one exemplary embodiment, the conversion
coated heat exchanger substrate (also called a conversion coated
heat exchanger) is subjected to a corrosion inhibitive
electro-coating 16 (or "e-coat" 16).
In an embodiment, e-coat 16 is a cathodic electrophoretic coating
process performed in a bath of de-ionized water. The bath includes
an organic corrosion inhibitor for supplementing the corrosion
protection. The conversion coated heat exchanger is used as a
cathode while the organic corrosion inhibitor is suspended in the
bath. In a non-limiting embodiment, the organic corrosion inhibitor
used is available from PPG.RTM. but, in other embodiments, other
similar corrosion inhibitors such as, for example, strontium
chromate pigment may also be used without departing from the scope
of the invention. E-coat 16 may be performed by applying a negative
DC charge to the chromium coated heat exchanger. The oppositely
charged polymer molecules in the bath are drawn to the cathodic
heat exchanger and deposit on the surface of the conversion coated
heat exchanger. In one embodiment, a charge is applied to coat the
conversion coated heat exchanger with a uniform layer of the
corrosion-inhibited electrophoretic coating having an average
thickness of about 25 .mu.m. The e-coated heat exchanger is dried
at elevated temperature and time sufficient to cure the polymer
coating. In an embodiment, the heat exchanger is dried for a time
between 20 minutes to 30 minutes at about 160 degree Celsius (about
433 Kelvin) to about 170 degree Celsius (about 443 Kelvin). In an
alternative embodiment, an anodic electrocoating may also be used
in lieu of cathodic electrocoating.
In an exemplary embodiment, following electro-coating 16, the
e-coated heat exchanger is subjected to surface coating process
including an application of a solvent borne solution containing a
corrosion inhibitive top coat 18. Particularly, the e-coated heat
exchanger is sprayed with a solution containing a liquid
polyurethane coating having pigments that include a corrosion
inhibitor. In one embodiment, the solvent borne solution contains,
for example, HybriCor.TM. 204 from WPC Technologies, Inc in
sufficient concentrations in order to suppress corrosion. In other
embodiments, similar corrosion inhibitors such as strontium
chromate pigment may also be used without departing from the scope
of the invention. Also, the topcoat 16 is cured (i.e.,
cured-to-touch) for 20 minutes at elevated temperature after
allowing solvents to flash off in an ambient environment. In
another embodiment, the topcoat 16 is cured for a time of between
30 minutes to 45 minutes at about 60 degree Celsius (about 333
Kelvin) to about 70 degree Celsius (about 343 Kelvin). As will be
appreciated by those of skill in the art, these surface
preparation, coating and post-treatment procedures are susceptible
to a wide array of alternatives. Thus, it is contemplated that any
number of other procedures and practices may likewise be utilized
to perform these processes of the aluminum alloy heat exchanger. In
one embodiment, the heat exchanger may include a chemical etching
to remove any oxide layers on the surface, followed by a conversion
coating process 14, followed by electro-coating 16. Lastly, the
heat exchanger surface is dried and dipped into a solvent bath for
corrosion inhibitive top coat 18.
The technical effects and benefits of exemplary embodiments include
a method for providing an adherent multi-layered coating with
substantial corrosion resistance on the substrate of the heat
exchanger. In embodiments, the method includes a surface
pre-treatment of the heat exchanger, a conversion coating, an
electro-coating process, and an optional surface coating of the
heat exchanger. The surface pre-treatment includes at least one
step to ensure that the surface of the heat exchanger is clean and
free of residues and foreign materials. Another coating process
enables a film of a trivalent chromium compound to be uniformly
coated on the aluminum alloy heat exchanger substrate using an
autocatalytic conversion coating process. Further, the heat
exchanger is electro-coated by applying a corrosion inhibitive film
on the substrate surface. Also, an optional topcoat application is
used to supplement the corrosion protection on the surface in a
solution containing an ultraviolet pigment, corrosion inhibitor and
polyurethane.
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. While the description of the present invention has
been presented for purposes of illustration and description, it is
not intended to be exhaustive or limited to the invention in the
form disclosed. Many modifications, variations, alterations,
substitutions, or equivalent arrangement not hereto described will
be apparent to those of ordinary skill in the art without departing
from the scope and spirit of the invention. Additionally, while
various embodiment of the invention have been described, it is to
be understood that aspects of the invention may include only some
of the described embodiments. Accordingly, the invention is not to
be seen as limited by the foregoing description, but is only
limited by the scope of the appended claims.
* * * * *